The present invention relates broadly to the purification of hydrofluorocarbons. More specifically, the present invention relates to the separation of an azeotrope of dichloromethane (HFC-32) and dichlorodifluoromethane (CFC-12).
Difluoromethane (HFC-32) is a hydrofluorocarbon developed to replace ozone-depleting hydrochlorofluorocarbons (HCFCs) or chlorofluorocarbons (CFCs) refrigerants/refrigerant blends. During the production of HFC-32, certain by-products are formed, including CFC-12, which is of particular interest herein. It has been found that CFC-12 and HFC-32 form a low-boiling azeotrope in the distillation of HFC-32.
Such an azeotropic cannot be separated using conventional distillation techniques. Furthermore, alternative methods of separating CFC-12 from HFC-32 such as extraction, extractive distillation, or absorption introduce higher costs and additional components to the purification process.
Although further recovery of HFC-32 tends to be difficult, it is nevertheless necessary to maintain high yields. For example, if no additional recovery of HFC-32 is performed on an azeotropic distillate containing about 9.2 wt % CFC-12 (as would be obtained through economical, high pressure distillation), then an HFC-32 yield loss of at least 10% can be expected. In other words, without further recovery, the HFC-32 yield would be less than 90%.
Therefore, a need exists for a process which recovers HFC-32 in high yield from the CFC-12/HFC-32 azeotropic distillate, but which does not involve costly and complex distillation techniques and apparatus. The present invention fulfills this need among others.